Oct 11, 2007
The intriguing possibility that a virus which causes cancer in mice could also spread in humans has been raised by laboratory scientists.
The Austrian-led team found that mouse mammary tumour virus (MMTV) - which causes breast cancer in the animals - could replicate in human cells.
Other cancer experts, however, said the results, in the journal Retrovirology, should be treated with caution.
They said there was little evidence to link it to human breast cancer.
Viruses are now known to be involved in the development of several cancers - including cervical and liver cancer.
MMTV was discovered in the 1930s, and has been previously suggested as a possible cause of human breast cancer.
However, even though traces of the virus have been found before in human breast cancer cells, attempts to prove a link have foundered in the past because no-one could find evidence that the virus could survive and replicate in that environment.
The latest research claims to have done this - they say MMTV 'rapidly spreads' in breast cancer cells in their laboratory.
Dr Stanislave Indik, who led the team, said: "Often, viruses infect cells but cannot replicate further.
"If they can replicate, the chances that they cause disease may be increased."
The researchers said that while not proving that the virus can cause breast cancer in real people, it "lends more weight" to theories linking the virus to the disease, and to other conditions such as the liver disease primary biliary cirrhosis.
They said that if the MMTV were to be proven, existing drugs such as the anti-HIV medication AZT would stop it replicating.
Other experts are no so convinced that MMTV is likely to be a culprit for the disease.
Epidemiologist Dr Rob Newton, from the charity Cancer Research UK, said: "This paper suggests that, under controlled laboratory conditions, a mouse virus can infect cultured cells derived from human breast tissue.
"It does not demonstrate that this actually happens in the real world, nor have the researchers shown that such infection leads to the development of cancer.
"At the present time, the overall evidence in this area does not support the view that MMTV is a cause of human breast cancer."
This was echoed by Dr Sarah Cant, from Breakthrough Breast Cancer, who said: "Although this research indicates the mouse mammary tumour virus can spread between breast cancer cells in the lab, there is still no concrete scientific evidence that the virus causes breast cancer in humans.
"Much more research would be needed before we can say whether or not MMTV can be passed from mice to humans to cause breast cancer."